Project description
The confinement of light by
plasmonic waveguides in nano-dimensions can be a source of considerable
nonlinearity when combined with an appropriate nonlinear material. In this
project we study nonlinear plasmonic waveguides, such as metallic stripes, grooves,
and wedges, in Lithium Niobate as well as in complex arrangements, as e.g.
couplers, arrays, splitters, and resonators, composed of such guides. It is our
purpose to understand and to control the ultrafast nonlinear dynamics of light
in these structures.
We explore the
possibilities to use the nonlinearity to overcome existing limitations of
metal-optics by compensating the plasmonic propagation losses of transmitted
signals by parametric gain. In extension, we also investigate nano-sized
optical parametric oscillators Furthermore complex plasmonic waveguide
structures are studied for the ultrafast control of optical near-fields on the
nano-scale.
The project comprises a
comprehensive scientific approach: State-of-the-art theoretical methods are
used and are further developed to simulate nonlinear plasmonic structures.
Advanced nanofabrication technologies are used to nanostructure Lithium Niobate
together with a number of noble metals. We equally employ a spectrum of
experimental techniques for the characterization of ultrafast processes using
near-field and far-field approaches.
(left) Nanostructured microwire waveguide from LiNbO3 and Pt for efficient cascaded nonlinear interactions. (center) Geometry of the plasmonic slot-waveguide with Lithium Niobate in its core and the field profiles of the lowest and second order eigenmode supported by the structure. (right) The generated second harmonic for the plasmonic slot-waveguide while considering the interaction of the lowest order mode at the fundamental frequency and the lowest order or the second order mode at the second harmonic.
Publications
Generation and near-field imaging of Airy surface plasmons
A. Minovich, A. Klein, N. Janunts, T. Pertsch, D. Neshev, and Y. Kivshar
Phys. Rev. Lett. 107 (2011) 116802
We demonstrate experimentally the generation and near-field imaging of nondiffracting surface waves, plasmonic Airy beams, propagating on the surface of a gold metal film. The Airy plasmons are excited by an engineered nanoscale phase grating, and demonstrate significant beam bending over their propagation. We show that the observed Airy plasmons exhibit self-healing properties, suggesting novel applications in plasmonic circuitry and surface optical manipulation.
Cascaded third harmonic generation in lithium niobate nano-waveguides
A. S. Solntsev, A. A. Sukhorukov, D. N. Neshev, R. Iliew, R. Geiss, T. Pertsch, and Y. S. Kivshar
Applied Phys. Lett. 98 (2011) 231110
We predict highly efficient third harmonic generation through simultaneous phase-matching of second-harmonic generation and sum-frequency generation in lithium niobate nanowaveguides, enabled due to strong modal dispersion. We demonstrate that the waveguide size which corresponds to phase-matching is also optimal for highest mode confinement and therefore for strongly enhanced conversion efficiency.
Integrating cold plasma equations into the Fourier modal method to analyze second harmonic generation at metallic nanostructures
T. Paul, C. Rockstuhl, and F. Lederer
Journal of Modern Optics 58 (2011) 438
We introduce a computational scheme to analyze second harmonic generation in periodic metallic nanostructures, i.e. metamaterials, that are composed of multiple layers. To describe the nonlinear polarization by the metallic constituents, we rely on a hydrodynamic model for the conduction electrons. Our computational approach is based on the Fourier modal method into which we incorporate the hydrodynamic plasma model. We detail physical and numerical peculiarities of the algorithm and we access aspects of convergence in a comprehensive manner. Finally, we provide further insights into the characteristics of intrinsic nonlinearities of metamaterials.
Long-distance indirect excitation of nanoplasmonic resonances
W. Khunsin, B. Brian, J. Dorfmüller, M. Eßlinger, R. Vogelgesang, C. Etrich, C. Rockstuhl, A. Dmitriev, and K. Kern
Nano Letters 11 (2011) 2765
In nanoscopic systems, size, geometry, and arrangement are the crucial determinants of the light-matter interaction and resulting nanoparticles excitation. At optical frequencies, one of the most prominent examples is the excitation of localized surface plasmon polaritons, where the electromagnetic radiation is coupled to the confined charge density oscillations. Here, we show that beyond direct near- and far-field excitation, a long-range, indirect mode of particle excitation is available in nanoplasmonic systems. In particular, in amorphous arrays of plasmonic nanodiscs we find strong collective and coherent influence on each particle from its entire active neighborhood. This dependency of the local field response on excitation conditions at distant areas brings exciting possibilities to engineer enhanced electromagnetic fields through controlled, spatially configured illumination.
Towards the Origin of the Nonlinear Response in Hybrid Plasmonic Systems
T. Utikal, T. Zentgraf, T. Paul, C. Rockstuhl, F. Lederer, M. Lippitz, and H. Giessen
Physical Review Letters 106 (2011) 133901
Plasmonic systems are known for their distinct nonlinear optical properties when compared to purely dielectric materials. Although it is well accepted that the enhanced nonlinear processes in plasmonic-dielectric compounds are related to the excitation of localized plasmon resonances, their exact origin is concealed by the local field enhancement in the surrounding material and the nonlinearity in the metal. Here, we show that the origin of third-harmonic generation in hybrid plasmonic-dielectric compounds can be unambiguously identified from the shape of the nonlinear spectrum.
Relating localized nanoparticle resonances to an associated antenna problem
S. Bin Hasan, R. Filter, A. Ahmed, R. Vogelgesang, R. Gordon, C. Rockstuhl, and F. Lederer
Phys. Rev. B 84 (2011) 195405
On an empirical basis, we indicate the possibility of conceptually unifying the description of resonances existing in some of the analytically studied metallic nanoparticles and optical nanowire antennas. To this end the nanoantenna is treated as a Fabry-P´erot-like resonator with arbitrary seminanoparticles forming the terminations. We show that the frequencies of the quasistatic dipolar resonances of the considered nanoparticles coincide with those where the round-trip phase of the complex reflection coefficient of the fundamental propagating plasmon polariton mode at the wire terminations amounts to 2π. The lowest order Fabry-P´erot resonance of the optical wire antenna occurs therefore even for a negligible wire length.
Generation of Hankel-type surface plasmon polaritons in the vicinity of a metallic nanohole
S. Nerkararyan, Kh. Nerkararyan, N. Janunts, and T. Pertsch
Phys. Rev. B 82 (2010) 245405
It is shown that the electromagnetic fields of surface plasmon polaritons (SPPs) generated around a nanohole, milled in a metal film, can be described by Hankel functions. These SPPs are dipole active and can be excited by a linearly polarized electromagnetic plane wave under normal incidence (with respect to the metal surface). Two kinds of Hankel-type SPPs are generated simultaneously around a nanohole: inward and outward propagating with respect to the nanohole. The wave fields of the Hankel-type SPPs increase anomalously in the close vicinity of the nanohole and exceed considerably that of the incident wave. It is shown analytically that the excitation cross section of Hankel-type SPPs, around a nanohole with excitation area limited by circular boundary, is significantly higher compared to the case of an infinite metal surface. We conclude that the unusually high transmission of light through arrays of nanoholes milled in a metal film can be ascribed to the excitation of inward Hankel-type SPPs, which transfer the energy toward the nanohole region.
A numerical approach for analyzing higher harmonic generation in multilayer nanostructures
T. Paul, C. Rockstuhl, and F. Lederer
J. Opt. Soc. Am. B 27 (2010) 1118
We introduce a computational scheme for analyzing higher harmonic generation in nonlinear optical periodic nanostructures that are composed of multiple layers. Such nanostructures, i.e., photonic crystals, plasmonic nanostructures, or metamaterials, are currently in the focus of interest to enhance the efficiency of various nonlinear processes. We exploit an adapted Fourier modal method combined with a modified scattering-matrix algorithm to numerically model these processes. We explicitly present a numerically stable formulation of the scheme. The strength and the applicability of the algorithm are outlined at some selected examples.
Plasmonic Nanowire Antennas: Experiment, Simulation, and Theory
J. Dorfmüller, R. Vogelgesang, W. Khunsin, C. Rockstuhl, C. Etrich, and K. Kern|
Nano Letters 10 (2010) 3596
Recent advances in nanolithography have allowed shifting of the resonance frequency of antennas into the optical and visible wavelength range with potential applications, for example, in single molecule spectroscopy by fluorescence and directionality enhancement of molecules. Despite such great promise, the analytical means to describe the properties of optical antennas is still lacking. As the phase velocity of currents at optical frequencies in metals is much below the speed of light, standard radio frequency (RF) antenna theory does not apply directly. For the fundamental linear wire antenna, we present an analytical description that overcomes this shortage and reveals profound differences between RF and plasmonic antennas. It is fully supported by apertureless scanning near-field optical microscope measurements and finite-difference time-domain simulations. This theory is a starting point for the development of analytical models of more complex antenna structures.
Plasmonic modes of extreme subwavelength nanocavities
J. Petschulat, C. Helgert, M. Steinert, N. Bergner, C. Rockstuhl, F. Lederer, T. Pertsch, A. Tünnermann, and E.-B. Kley
Opt. Lett. 35 (2010) 2693
We study the physics of a new type of subwavelength nanocavities. They are based on U-shaped metal–insulator–metal waveguides supporting the excitation of surface plasmon polaritons. The nanocavity arrays are excited by plane waves at either a normal or oblique incidence. Because of their finite length, discrete modes emerge within the nanocavity. We show that the excitation symmetry with respect to the cavity ends permits the observation of even and odd modes. Our investigations include near- and far-field simulations and predict a strong spectral far-field response of the comparably small nanoresonators. The strong near-field enhancement observed in the cavity at resonance might be suitable to increase the efficiency of nonlinear optical effects and quantum analogies and might facilitate the development of optical elements, such as active plasmonic devices.
